1. Field of the Invention
The present invention relates generally to drill bits for drilling into a subterranean formation, and more specifically to drill bits for drilling into a subterranean formation that include a wear resistant coating applied to the inner surface of the drill bit.
2. Description of Related Art
Rotary-type drill bits include both rotary drag bits and roller-cone bits. Typically, in a rotary drag bit, fixed cutting elements are attached to the face of the drill bit. In a roller-cone arrangement, the bit typically has three cones, each independently rotatable with respect to the bit body supporting the cones through bearing assemblies. The cones carry either integrally formed teeth or separately formed inserts that provide the cutting action of the bit.
The roller cones are typically attached to a bearing shaft that extends in a generally inward and downward orientation relative to the leg of the drill bit. Rotation of the roller cone is generally about an axis defined by the bearing shaft. The roller cone typically contacts the bearing shaft at a plurality of interior surfaces of the roller cone. The force applied to the drill bit during drilling operations is transmitted through the drill bit and to the interior surfaces of the roller cone and the bearing shaft.
While hardened and wear resistant coatings have been previously applied to the outer wear surfaces of drill bits, such as for example, the cutting elements, the interior wear surfaces of drill bits generally do not receive these surface treatments. Wear on the interior contacting surfaces can lead to the deterioration of the interior of the roller cone and/or the bearing shaft it contacts, thus leading to the need to replace the drill bit. Thus a need exists for a wear resistant surface coating to be applied to the surfaces of the interior of the roller cone and/or bearing shaft.